Geoscience Reference
In-Depth Information
Table 6.5
User's Accuracy in Study Area,
Rondonia 1986-1999
Classified Data
1986
1994
1999
Forest
89.8%
93.5%
96.7%
Secondary forest
45.5%
63.1%
77.4%
Transition
42.9%
75.0%
57.5%
Crops
25.0%
53.6%
67.5%
Pasture
80.0%
77.5%
89.6%
Bare Soil
66.7%
28.7%
Water
100.0%
100.0%
93.6%
Overall accuracy
84.6%
88.3%
89.0%
Kappa statistic
0.52
0.69
0.78
6.3.2
Map Accuracy Assessment
The user's accuracy is summarized in Table 6.5. The increase in overall map accuracies for each
subsequent year in the analysis was attributed to several factors. First, we used three different sensors
(MSS, TM, and ETM
), which introduced increased spatial and spectral resolution of the sensors
over time. Second, the 1986 MSS image had clouds that introduced some classification errors. Third,
collecting retrospective data was a challenge because interviewees sometimes had difficulty recalling
LC and associated LU practices over the study period. In general, retrospective LU information had
a higher level of uncertainty than for time periods closer to the date of the interview.
Despite these difficulties, however, overall accuracy was between 85 and 89% for 1986 and
1999, respectively. Accuracy for specific classes ranged between 50 and 90%, achieving
+
96%
for primary forest in 1999. Some bare soil (1999) and crops (1986) classes were particularly difficult
to map and attained accuracies below 30%. The sample size for these particular cover types was
relatively small, which may have contributed to this poor outcome. When coupled with the fact
that areas of bare soil and crops tend to be small in the study area (
1.0 ha), the lower accuracies
were not unexpected for these classes. Error matrices for 1994 and 1999 are presented in Tables
6.6 and 6.7, respectively. The overall accuracy for 1999 was 89.0% (Kappa 0.78). With the exception
of bare soil, all the remaining classes had user's accuracies that ranged from 57.5 to 96.7% and
producer's accuracies between 66.5 and 100.0%. The overall accuracy for the 1994 land-cover map
was 88.3%. In general, accuracy for specific cover types ranges between 50 and 90%, achieving a
high of 96.7% for primary forest in 1999. The bare soil (1999) accuracy was below 30%; however,
the limited proportion of training sample pixels relative to the total amount of pixels comprising
the study area for this specific class may have contributed to this poor outcome.
£
Table 6.6
Error Matrix for the Land-Cover Map in Study Area, Rondonia 1994
Reference Data
Sec.
Forest
Bare
Soil
User's
Accuracy
Classified Data
Forest
Transition
Crops
Pasture
Water
Total
Forest
1218
76
0
5
0
1
3
1303
93.5%
Secondary forest
40
82
0
6
1
1
0
130
63.1%
Transition
0
0
9
3
0
0
0
12
75.0%
Crops
9 5
1
30
0
1
0
56
53.6%
Pasture
15
0
0
6
79
1
1
102
77.5%
Bare soil
4
0
0
5
0
18
0
27
66.7%
Water
0
0
0
0
0
0
25
25
100.0%
Total
1286
173
10
55
80
22
29
1655
Producer's accuracy
94.7%
47.4%
90.0%
54.6%
98.8%
81.8%
86.2%
Note:
Overall classification accuracy = 88.3%. Kappa statistic = 0.69.
 
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